FUEL CELLS—ENERGY FOR A POWER-HUNGRY WORLD - Chemistry: Notable Research and Discoveries - page 151

chapter 2, which have a shell and an interior. This material is deposited
on carbon electrodes. Strasser and his coworkers discovered that send-
ing a varying electric current through the electrode separated most of
the other metals from the shell, leaving the nanoparticle with mostly
platinum on the surface. Surfaces are important because this is where a
lot of catalytic activity takes place, and a collection of nanoparticles has
a lot more surface area than the same amount of material in bulk. Yet
Strasser believes the increase in surface area is not enough to account
for all of the elevated activity rates, and the structure of the nanoparticle
surfaces may contribute as well. Further research into this process may
produce even greater efficiencies.
Another issue with platinum catalysts is that their capacity some-
times fades over time. Several factors are responsible, including a
phenomenon similar to the side effects described for medications in
chapter 3. Side effects occur when a medication acts on healthy tissue
instead of the intended target. With platinum electrodes, the problem
is that sometimes unwanted reactions occur at the electrodes. In the
oxygen reactions taking place at the cathode, for example, hydroxide
(OH) and other molecules sometimes form and bind to the platinum
atoms. These molecules cover the platinum atoms and block access to
the desired reactant, thereby reducing the catalytic activity. Sometimes
the molecules even pull platinum atoms away from the surface, causing
serious electrode degradation.
This problem is exacerbated when power requirements fluctuate.
For instance, a fuel cell in an automobile would experience frequent
stops, especially in city traffic, and platinum electrodes would rapidly
lose their catalytic function.
But now researchers at Brookhaven National Laboratory in New York
have found a method to stabilize platinum electrodes. The researchers
used platinum nanoparticles as electrodes but modified the nanoparticles
with the addition of thin layer of gold (Au). With scanning tunneling
microscope (STM), described in chapter 2, and X-ray analysis, described
in chapter 1, the research team determined that the gold formed clusters
that protected the platinum from the attack of oxides. The gold-plated
catalysts performed well more than 30,000 cycles of voltages varying from
0.6 to 1.1 volts. Junliang Zhang, Kotaro Sasaki, Eli Sutter, and Radoslav
Adzic published this research in a paper, “Stabilization of Platinum Oxy-
gen-Reduction Electrocatalysts Using Gold Clusters,” in a 2007 issue of